For a long time it has been a main target in conducting research and development of resins to find a technique to improve flame retardancy of thermoplastic resins. So far, a variety of compounds have been proposed as a flame retardant agent. Flame retardant agents, which are generally used in the thermoplastic resin field, include a flame retardant agent based on a halogenic compound, particularly, a bromic compound, and a phosphorus flame retardant agent based on phosphoric acid ester. Such flame retardant agents are used with a fluorinated polyolefin as a anti-drip agent or an antimony compound as a flame retardation assistant.
However, as concerns about the environmental issue increase, there is a trend to restrain the use of the halogen based flame retardant agent. Therefore, the phosphorus flame retardant agent, which is free of any halogen compound, is preferred to the flame retardant agent. Such a phosphorus flame retardant agent includes monomeric aromatic phosphoric acid ester compounds such as triphenyl phosphate, tricresyl phosphate and the like. The flame retardant agenots comprising the monomeric aromatic phosphoric acid ester compounds can provide excellent flame retardancy and desired mechanical properties. However, such a flame retardant agent tends to migrate to the surface of a molded article during a molding process, thereby causing a juicing phenomenon. Furthermore, there is a disadvantage in that heat resistance of the resultant resin composition is remarkably reduced.
Accordingly, in order to overcome the above-mentioned problems, Japanese Patent Laid-Open Publication Nos. Sho59-24736, Sho59-45351, and Sho59-202240 disclose the use of an oligomeric condensed phosphoric acid ester compound as a flame retardant agent for thermoplastic resins. The disclosed flame retardant agents have advantages in that they involve a reduced juicing phenomenon while relatively improving the heat resistance of the resultant resin when they are applied to thermoplastic resins. However, they exhibits a reduced flame retardancy, as compared to that obtained when the same amount of the flame retardant agent based on the monomeric phosphoric acid ester is used. Therefore, it is needed to add the flame retardant agent in an increased amount so as to achieve an equal level of flame retardancy.
Phosphoramide flame retardants are disclosed in Japanese Kokai Publication No. 2000-154277 including phenyl morpholide monophosphate compounds. These compounds are disclosed as flame retardants suitable for use with various synthetic resins. The synthesis of diphenyl morpholide monophosphate and dimorpholide phenyl monophosphate is described. There is no disclosure of derivatives of the monophosphates or reacting the monophosphates with any other compounds.